This application claims the priority of German application No. 100 35 763.6, filed Jul. 22, 2000, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a device for metering a gaseous medium, in particular air.
The general prior art has disclosed motor vehicles with fuel cell systems which supply at least part of the energy required in the motor vehicle. In particular, one should mention fuel cell systems which generate the hydrogen-containing gas required for operation of the fuel cell from a hydrocarbon in the fuel cell system itself. These gas generation systems have numerous individual components, of which purely by way of example oxidation stages, reforming reactors and shift stages should be mentioned at this point.
Many of the components of a fuel cell system of this type, in particular with an integrated gas generation system, require a metered supply of gaseous media, in particular of air or another oxygen-containing gas, to supply oxygen for the chemical and electrochemical operations in the fuel cell system.
Since this metered supply of gaseous media generally has to take place very precisely and at a controlled time into the appropriate component of the fuel cell system, a fuel cell system of this type usually has a dedicated metering valve for each of the components. These metering valves, which, by way of example, use a Laval nozzle element and a nozzle needle to allow a targeted, controllable metering of gaseous media, are assigned to the respective component. Determining the most important variables, for example upstream of the metering valve, provides the measured values which are required in order to control the metering valves by means of suitable software.
If a fuel cell system of this type is now fitted in a motor vehicle, the drawback arises that a metering valve is arranged on each of numerous components. These metering valves must in each case be provided with suitable sensor and cabling means and suitable lines for supplying it with the gaseous medium, which is generally been compressed beforehand. On account of the often very restricted spatial conditions which are present when the system is installed in a motor vehicle, this represents a considerable drawback and leads to a very high degree of outlay regarding the line elements which need to be laid for the purpose of guiding the compressed, gaseous medium from a compressor unit or the like to the metering valves. Moreover, there is a considerable drawback in terms of the laying and the required line lengths of the corresponding sensors which would have to be assigned to each of the metering valves.
Further drawbacks arise with regard to the thermal load on the metering valves. Since the metering valves are in each case arranged close to the component in question, there are highly divergent temperature loads imposed on the individual metering valves. For example, a metering valve which is arranged in the region of the gas generation system will experience a far higher thermal load than a metering valve arranged in the region directly upstream of the fuel cell. When using metering valves of identical design, this leads to different levels of thermal expansion of the elements of the individual metering valves and therefore to a considerable control outlay, since when these metering valves, which are of identical design but are exposed to different thermal conditions, are activated, there may be different relationships between mass throughput, control times and the electrical characteristic variables.
Therefore, the object of the invention is to provide a device for metering a gaseous medium, having a plurality of metering valves, into a plurality of components of a fuel cell system in a motor vehicle which reduces the space required and avoids differing loads, in particular thermal loads, but also loads caused by vibrations or the like, on the metering valves.
This object is achieved by the device according to the present invention.
A central middle block, on which all the metering valves are arranged, results in considerable advantages in terms of the packaging of the fuel cell system in the motor vehicle. A central arrangement of the metering valves on the middle block and the fact that they are each connected to at least one passage, which is connected to the at least one inlet opening for the gaseous medium, at their respective connection points result in a central supply system which supplies all the metering valves with the pressurized, gaseous medium. The gaseous medium is supplied, for example, via a compressor unit. The required length of line between the compressor unit and the individual metering valves which, in order to avoid pressure losses upstream of the metering valves, should have the largest possible diameter is reduced to a minimum, and the distribution takes place in the central middle block itself.
The previous complexity of laying lines with a maximum possible diameter which, if appropriate, additional measurement lines of the sensor arrangement positioned in the vicinity of the metering valves, lead to large amounts of space being taken up and caused a xe2x80x9cchaoticxe2x80x9d arrangement of lines in the fuel cell system. By contrast, in the device according to the present invention, in which all the metering valves are centralized, only the lines which have a very much smaller diameter for conveying the metered medium have to be laid, and all the sensors can be concentrated in the region of the central metering device.
In addition to these considerable advantages of the device according to the present invention in terms of packaging, further advantages arise from the central arrangement of all the metering valves of the fuel cell system at one location. The fact that all the metering valves are situated within a spatially very small area means that they are exposed to approximately the same external conditions (i.e., the same temperature, the same effects from shaking and vibrations and the like) so that if the metering valves are controlled appropriately it is possible to ensure that each of the individual metering valves functions identically to the others.
Moreover, a further advantage of the device according to the present invention is that, on account of the metering valves being arranged centrally around the middle block, the metering valves can be installed, for example, in a position within the fuel cell system which is highly advantageous for any maintenance which may be required on the metering valves.
In an embodiment of the present invention, sensors that can be used to detect variables of the gaseous medium are arranged in the at least one passage.
This has the advantage that a single set of sensors for the at least one passage can be used to carry out a central measurement, so that relatively good characteristic values of the gaseous mediums supplied to the metering valve can be determined for all the metering valves used. Because the lengths of line which are present in the region of the middle block between the sensors and the respective connection points of the metering valves are only very short, there is practically no distortion of the measured variables of the gaseous medium supplied.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.